The invention relates to a transmission arrangement, in which a continuously variable toroidal drive mechanism, an intermediate planetary gear train and a final planetary gear train are arranged in the power path between an input shaft and an output shaft.
In a known transmission arrangement of this type (U.S. Pat. No. 6,059,685) a central intermediate shaft is connected to the input shaft, to a central toroidal drive disc of the toroidal drive mechanism and to the two-armed planet carrier of the intermediate gear train supporting double planet wheels. A concentric intermediate shaft, through which the central intermediate shaft extends with radial clearance, connects a central toroidal driven disc of the toroidal drive mechanism to a sun gear of the intermediate gear train, which has a drive connection containing a clutch with a first mechanism link in the form of a sun gear of the final gear train. The two concentric intermediate shafts create two central torque paths for the passage through the toroidal drive mechanism, thereby permitting a fundamentally coaxial arrangement of input and output shafts and also of the three gear trains, were the toroidal drive mechanism to be equipped with only one toroidal drive disc and one toroidal driven disc.
In order to also achieve the parallel connection of two central toroidal drive discs and two central toroidal driven discs, otherwise common in toroidal drive mechanisms, with a fundamentally coaxial arrangement of all the said transmission components, in the known transmission arrangement the concentric intermediate shaft is also connected in parallel with the second driven disc, and the one arm of the planet carrier of the intermediate gear train carrying the secondary planet wheels is also connected in parallel to the second drive disc of the toroidal drive mechanism. Furthermore, in the known transmission arrangement, in order to be able to bring the sun gear of the intermediate gear train connected to the concentric shaft into drive connection with the sun gear forming the first mechanism link of the final gear train, the other arm of the planet carrier, carrying the main planet wheels meshing with the secondary planet wheels, is connected by a radial drive arm to the central intermediate shaft, and two inner central gears meshing with the main planet wheels are arranged on both sides of the radial drive arm, one of the sun gears being connected to the concentric intermediate shaft and the other sun gear having the drive connection, containing an engageable and disengageable clutch, to the sun gear forming the first mechanism link of the final gear train.
The secondary planet wheels of the intermediate gear train in turn mesh with an ring gear, which has a drive connection, including an engageable and disengageable clutch, to a second mechanism link in the form of a planet carrier of the final gear train carrying double planet wheels, the carrier in turn also being connected to the output shaft.
Whilst in the final gear train of the known transmission arrangement one of each of the two intermeshing single planet wheels that form a double planet wheel meshes with the sun gear provided as the first mechanism link of the final gear train, the ring gear meshing with each of the other single planet wheels is fixed so that it cannot rotate in relation to a non-rotating part of the housing, as a third mechanism link of the final gear train.
In the known transmission arrangement the clutch connecting the outer ring gear of the intermediate gear train to the planet carrier of the final gear train is engaged in the bottom low-speed range and in reverse gear, whilst the clutch connecting the second sun gear of the intermediate gear train to the sun gear of the final gear train is engaged in the adjoining upper higher-speed range.
An inherent feature of a toroidal drive system is the reversal in the direction of rotation between input and output, because it is in principle a planetary gear train with firmly braked planet carrier, in which the planet wheels, here known as xe2x80x9crollersxe2x80x9d, each in frictional contract with a toroidal central drive and driven disc, are mounted so that they can swivel about a swivel axis perpendicular to their axis of rotation but are otherwise immovably fixed in their position relative to the central axis. Since in the known transmission arrangement in the upper drive range the final gear train is driven directly by the output of the toroidal drive mechanism, the final gear train in this drive range must have a negative transmission ratio in forward drive, which is achieved by the double planet wheels, which at high road speeds, however, have high rotational speeds in relation to their planet carrier. In the lower drive range, too, the efficiency of the known transmission arrangement is low, because the output shaft is driven directly by the outer central gear of the intermediate gear train, thereby obviating the need for a final gear train, the latter nevertheless also giving rise to power losses in this drive range owing to its braked outer ring gear, and its sun gear thereby being geared up in relation to the output shaft.
The object of the invention is essentially to create a transmission arrangement with a high efficiency, in which a toroidal drive mechanism, an intermediate planetary gear train and a final planetary gear train are arranged in the power path between an input shaft and an output shaft with a fundamentally coaxial alignment of the transmission components.
In a transmission arrangement including a continuously variable toroidal drive mechanism, an intermediate planetary gear train and a final planetary gear train which are arranged in the power path between an input shaft and an output shaft, a central intermediate shaft is connected to the input shaft and to a central drive disc of the toroidal drive mechanism, and to a planet carrier of the intermediate gear train. A concentric intermediate shaft, through which the central intermediate shaft extends, is connected to a central driven disc of the toroidal drive mechanism and to a sun gear of the intermediate gear train. The concentric intermediate shaft has a drive connection to a first mechanism link of the final gear train in the form of a sun gear. An outer ring gear of the intermediate gear train has a drive connection to a second mechanism link of the final gear train. A third mechanism link of the final gear train is mounted on a housing part. A fourth mechanism link of the final gear train has a drive connection to the output shaft, this arrangement providing for high efficiency with a coaxial arrangement of the transmission components.
In the transmission arrangement according to the invention, the final gear train has a fourth mechanism link for driving the output shaft, it being possible to integrate the link into the transmission mechanism by way of a second toothed rim of the planet wheels or by means of an additional final planetary gear train with a common planet carrier for both final gear trains.
In the transmission arrangement according to the invention, the number of teeth situated in the power flow of the upper drive range is reduced to a minimum in order to achieve the same directions of rotation of input shaft and output shaft in forward drive and a fundamentally coaxial design for the arrangement.
In the transmission arrangement according to the invention, the rotationally fixed planet carrier achieves the function of an ordinary gear train without clutch power flows for the final gear train(s), thereby increasing the efficiency in the upper drive range affecting consumption, and thus obtaining a reduction in the fuel consumption.
In the transmission arrangement according to the invention, the use of a planet wheel with two toothed rims having an equal or unequal number of teeth in the final gear train means, on the one hand, that the rotational speeds of the planet wheel in relation to the planet carrier can be kept low and, on the other, that identical planet wheels can be provided in intermediate gear train and final gear train, which results in identical bearing pins, friction washers, bearings and sun gears and gear rings, etc.
In the transmission arrangement according to the invention, the main planet wheels in the intermediate gear train can be designed with toothed rims having different numbers of teeth. In an advantageous embodiment the toothed rim meshing with the second inner central gear, which by way of the one clutch can be brought into drive connection with the sun gear forming the first mechanism link of the final gear train, has the greater number of teeth, so that higher rotational speeds occur at the input of the final gear train than at the output of the toroidal drive mechanism. A spread of 4.5, for example, can thereby be achieved for the transmission arrangement with a spread of 5.5 for the toroidal drive mechanism in the upper drive range, that is to say the reduction in the spread is significantly less in the transmission arrangement according to the invention than in known transmission arrangements. Furthermore, a power division is achieved in the transmission arrangement because of the differing numbers of teeth. A constant power component is transmitted by way of the direct path of the central intermediate shaft 10 and a variable power component by way of the toroidal drive mechanism 7, which is subjected to reduced load and can therefore be of smaller dimensions. Since the efficiency of the direct path is greater than that of the toroidal drive mechanism, this also results in increased overall efficiency.
In the transmission arrangement according to the invention, in the embodiment having an additional final planetary gear train, transmission of the first drive range by means of the additional final gear train permits optimization of the individual transmission ratios in the transmission arrangement. A slight reduction in efficiency due to the additional tooth engagements and its effect on fuel consumption may be disregarded in view of the small length of time spent in the lower drive range as a proportion of total vehicle operating time. In particular, it is possible by means of the additional final gear train to design the transmission ratios so that the dynamic neutral condition, in which the rotational speed of the output shaft is equal to zero, lies in the area of a transmission ratio of the toroidal drive mechanism of xe2x88x921 and hence in the highest load capacity range. Furthermore, the additional final gear train permits optimization of the transmission range of the upper drive range with regard to consumption.
In the transmission arrangement according to the invention, there appears to be an increase in the design cost owing to the additional gear plane, but it also provides a reduction in the overall length of the arrangement. If the output shaft is driven by an outer ring gear of the final drive train, for example, the parking position gear can be rotationally fixed to this ring gear and therefore incorporated into the arrangement with no need for additional overall axial space. Since in the transmission arrangement according to the invention the planet carrier of the final gear train is fixed to the housing, the transmission shafts can be advantageously supported, which likewise leads to a reduction in the axial length of the arrangement. Furthermore, it is possible in the transmission arrangement according to the invention to direct the oil supply to the transmission shafts by way of the fixed planet carrier, which also proves advantageous in the desired shortening of the overall length of the arrangement. Finally the roller bearing arrangement supporting the output shaft at its output flange end in relation to the housing and the outer central gear drive connected to the output shaft can be arranged in the same axial area of the axis of rotation of the output shaft, so that a compact design and a short overall length are achieved.